For the entire history of the treatment of waste products produced by the bodies of animals or mankind, a naturally occurring process has been the basis for the treatment of carbon-based and other compounds that make up the body waste. The presence of several types of bacteria which are included in the waste body products from all animals and mankind have provided the means of treatment by either of two biological processes. One class of naturally occurring bacteria utilizes any dissolved oxygen in the water phase of the waste to oxidize the waste products with the resulting production of water, carbon dioxide and other oxide products. If the waste liquid phase does not contain dissolved oxygen, the second class of naturally occurring bacteria is able to act on the carbon-based and other compounds with the resulting production of hydrogen sulfide, methane and other complex organic compounds.
The general classification for the bacteria that require dissolved oxygen in the liquid phase of the waste water for growth is aerobic bacteria. Due to the very low solubility of oxygen in water, air must be in contact with the wastewater on a frequent cycle basis in order to resupply the dissolved oxygen in the wastewater. The second naturally occurring general class of bacteria is anaerobic bacteria which is based on the requirement that there cannot be any amount of dissolved oxygen in the wastewater for its growth to occur.
As the by-products produced by the aerobic bacteria growth in wastewater do not present a danger or provide an unacceptable secondary problem to mankind, it has in almost all cases become the primary process for wastewater treatment. The planned use of the second naturally available bacteria, anaerobic, has been confined to situations that lend themselves to the use of closed tanks or underground containers. The by-products produced by the action of the anaerobic bacteria result in major problems in the area of explosion hazard, corrosion problems, offensive odor and toxic reaction to mankind. The past and current processes for the treatment of wastewater are based on the use of the naturally occurring bacteria in either the aerobic bacterial cycle or the anaerobic bacterial cycle with the design of the treatment system being controlled by the ability to provide the most efficient environment for either type of bacterial growth. This design factor has to also have as a major consideration the disposal of the by-products of the bacterial action.
The treatment of wastewater does not begin at the treatment plant and this factor has become a major problem as the size of collection and transmission systems have been increased to minimize the number of treatment plants required. The action of the naturally occurring bacteria begins at the point of introduction of the body waste products into a water carrier. The growth of the aerobic bacteria is normally the first action as most wastewater liquid phases will contain some amount of dissolved oxygen. If the dissolved oxygen level is not maintained at some positive value, the growth of the aerobic bacteria will stop and be replaced by the growth of dormant anaerobic bacteria. The action of the aerobic bacteria is a self-limiting factor based on the availability of dissolved oxygen in the liquid phase. The lower the concentration of dissolved oxygen in the liquid phase, the slower the growth rate of the aerobic bacteria. Increases in the retention time in the collection and transmission systems associated with the treatment plant affects the condition of the wastewater received and the treatment process used. Without the wastewater being exposed to air contact, the loss of dissolved oxygen concentration can result in wastewater being received at the treatment plant in a condition that can adversely affect the normally used aerobic process.
Since a means for effectively controlling dissolved oxygen levels to a sufficient level in the collection and transmission systems was not previously available, the final treatment process was limited to the continuation of the process provided by natural occurrence. Only the selection of the type of aerobic or anaerobic process to continue the biological treatment could be utilized in wastewater treatment plants.
Three types of aerobic biological treatment processes are the most commonly found in wastewater treatment plants: the extended aeration process, the contact stabilization process and the complete mix process. All three processes utilize aeration devices to increase the dissolved oxygen concentration of the liquid phase of the wastewater and the return of wastewater solids with high concentrations of bacteria growth. The main differences between the three processes is the amount of retention time of the wastewater in the aeration zones of the treatment process, the amount of return of wastewater solids with high bacterial growth and the amount of wastewater solids that remain to be disposed of after the aeration process. The problem of disposal of the excess wastewater solids or sludge resulting from any of the three biological treatment processes has become a major threat to not only mankind, but also to the entire planet by destruction of the water supply necessary for both animal and human life. The amount of sludge generated by the three different biological processes is generally in the same ratio as the amount of retention time utilized in the aeration zones of the treatment process. For all three of the processes used, secondary treatment of sludge by either aerobic or anaerobic bacterial action is required The greater the amounts of sludge developed by the short retention times in the aeration zones of the treatment process, the greater the production of hazardous sludge that will require secondary treatment and controlled disposal.
The development of the centrifugal oxygenator described in U.S. patent application Ser. No. 07/109,192 filed Oct. 16, 1987 (which is a continuation of U.S. patent application Ser. No. 06/799,104 filed Nov. 18, 1985, now abandoned) and pending PCT application PCT/US86/02542, the contents of each of which are incorporated herein by reference, now provides the means to control the dissolved oxygen levels in wastewater collection and transmission systems which, in turn, allows the control of the naturally occurring bacterial growth. The centrifugal oxygenator has prove by certified testing that it has the ability to provide oxygen transfer rates of 40% in liquid levels of only two feet to as high as 98% at liquid levels of over twenty feet. Unlike prior aeration devices, the centrifugal oxygenator provides complete control of the air or gas flow rate from 0% to the maximum capacity of the unit size. The centrifugal oxygenator can operate on a stop/start basis without any clogging of the air or gas flow passages and also provides a high velocity directionalized mixing and solid suspension hydraulic flow from the unit